U.S. patent number 6,615,789 [Application Number 10/181,064] was granted by the patent office on 2003-09-09 for piston for internal combustion engines.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Akira Inoue, Nobuhisa Jingu.
United States Patent |
6,615,789 |
Inoue , et al. |
September 9, 2003 |
Piston for internal combustion engines
Abstract
A piston for an internal combustion engine, including a piston
crown having a central axis, and a piston bowl disposed in the
piston crown, on which two tumble flows of air are provided. The
piston bowl has a generally V-shaped contour in section taken along
a vertical plane intersecting the tumble flows, on which the two
tumble flows are retained at an inclined state toward a central
axis of the piston crown.
Inventors: |
Inoue; Akira (Yokohama,
JP), Jingu; Nobuhisa (Shizuoka, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
18873001 |
Appl.
No.: |
10/181,064 |
Filed: |
July 12, 2002 |
PCT
Filed: |
November 30, 2001 |
PCT No.: |
PCT/JP01/10474 |
PCT
Pub. No.: |
WO02/05584 |
PCT
Pub. Date: |
July 18, 2002 |
Foreign Application Priority Data
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Jan 12, 2001 [JP] |
|
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2001-004875 |
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Current U.S.
Class: |
123/193.6;
123/302; 123/307; 123/308 |
Current CPC
Class: |
F02F
1/4214 (20130101); F02F 3/26 (20130101); F02B
23/104 (20130101); F02B 31/085 (20130101); F02B
2031/006 (20130101); F02B 2075/125 (20130101); F02F
2001/245 (20130101); Y02T 10/12 (20130101); F02B
17/00 (20130101); F02B 2023/106 (20130101) |
Current International
Class: |
F02B
31/00 (20060101); F02F 1/42 (20060101); F02B
23/10 (20060101); F02B 31/08 (20060101); F02F
3/26 (20060101); F02B 17/00 (20060101); F02B
75/00 (20060101); F02F 1/24 (20060101); F02B
75/12 (20060101); F02B 031/00 () |
Field of
Search: |
;123/193.6,302,307,308,309,301,432 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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197 13 030 |
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Oct 1997 |
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DE |
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1 006 265 |
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Jun 2000 |
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EP |
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Other References
Patent Abstracts of Japan, vol. 1996, No. 5, May 31,1996 & JP
08-014048 (Mitsubishi Motors Corp.), Jan. 16, 1996. .
Patent Abstracts of Japan, vol. 2000, No. 9, Oct. 13, 2000 & JP
2000-154724 (Nissan Motor Co. Ltd.), Jun. 6, 2000. .
Patent Abstracts of Japan, vol. 2000, No. 15, Apr. 6, 2001 & JP
2000 345847 (Nissan Motor Co. Ltd.), Dec. 12, 2000..
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Primary Examiner: McMahon; Marguerite
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A piston for an internal combustion engine, comprising: a piston
crown having a central axis; and a piston bowl disposed in the
piston crown, on which two tumble flows of air are provided, the
piston bowl having a contour in section taken along a vertical
plane intersecting the tumble flows, the contour including an
inclined portion inclined toward the central axis of the piston
crown, the two tumble flows being disposed at the inclined
portion.
2. The piston as claimed in claim 1, wherein the contour of the
piston bowl is a generally V-shape including two opposed linear
portions linearly and inclinedly extending to be joined
together.
3. The piston as claimed in claim 2, wherein the piston bowl
comprises a bottom wall and side walls which cooperate to define
the generally V-shaped contour of the piston bowl, the bottom wall
including opposed and inclined bottom wall portions forming a
V-shaped contour, the side walls being connected with opposed outer
peripheries of the bottom wall portions.
4. The piston as claimed in claim 3, wherein the side walls are
inclined toward the central axis of the piston crown.
5. The piston as claimed in claim 3, wherein the bottom wall
portions are inclined at an angle of approximately 7 degrees
relative to a horizontal plane of the piston crown which is
perpendicular to the central axis of the piston crown.
6. The piston as claimed in claim 4, wherein the side walls are
inclined at an angle of approximately 10 degrees relative to a
plane parallel to the central axis of the piston crown.
7. A piston for an internal combustion engine, comprising: a piston
crown having a central axis; and a piston bowl disposed in the
piston crown, on which two tumble flows of air are provided, the
piston bowl including a bottom wall and opposed and inclined side
walls connected with the bottom wall, the side walls being opposed
to each other and inclined toward the central axis of the piston
crown.
8. The piston as claimed in claim 7, wherein the side walls are
inclined at an angle of approximately 10 degrees relative to a
plane parallel to the central axis of the piston crown.
9. A piston for an internal combustion engine, comprising: a piston
crown including an intake side and an exhaust side; and a piston
bowl disposed in the piston crown, the piston bowl having a
generally V-shaped section taken along a vertical plane
perpendicular to a direction extending from the intake side of the
piston crown toward the exhaust side thereof.
10. The piston as claimed in claim 9, wherein the piston crown has
a central axis, the piston bowl comprising a bottom wall having a
V-shaped section that forms a part of the generally V-shaped
section of the piston bowl, the bottom wall including opposed and
inclined bottom wall portions opposed to each other and inclined
toward the central axis of the piston crown.
11. The piston as claimed in claim 10, wherein the piston bowl has
side walls connected with opposed outer peripheries of the bottom
wall portions and inclined toward the central axis of the piston
crown.
12. The piston as claimed in claim 10, wherein the bottom wall
portions are inclined at an angle of approximately 7 degrees
relative to a plane perpendicular to the central axis of the piston
crown.
13. The piston as claimed in claim 11, wherein the side walls are
inclined at an angle of approximately 10 degrees relative to a
plane parallel to the central axis of the piston crown.
14. The piston as claimed in claim 10, wherein the bottom wall
portions have a junction at which the bottom wall portions are
joined together, the junction extending substantially across the
central axis of the piston crown.
15. An internal combustion engine, comprising: a cylinder chamber;
a cylinder head enclosing the cylinder chamber; a piston within the
cylinder chamber, the piston cooperating with the cylinder chamber
and the cylinder head to form a combustion chamber; at least two
intake ports in the cylinder head, communicating with the
combustion chamber to introduce air into the combustion chamber; at
least two exhaust ports in the cylinder head, communicating with
the combustion chamber; an intake air control valve in each of the
at least two intake ports, operative to deflect the air and create
two tumble flows of the air in the combustion chamber; a fuel
injector in the cylinder head, operative to directly inject fuel
into the combustion chamber; a spark plug in the cylinder head,
operative to ignite an air-fuel mixture in the combustion chamber;
wherein the piston includes: a piston crown having a central axis;
and a piston bowl disposed in the piston crown, on which the two
tumble flows of air are provided, the piston bowl having a contour
in section taken along a vertical plane intersecting the tumble
flows, the contour including an inclined portion inclined toward
the central axis of the piston crown, the two tumble flows being
disposed at the inclined portion.
16. The internal combustion engine as claimed in claim 15, wherein
the contour of the piston bowl is a generally V-shape including two
opposed linear portions linearly and inclinedly extending to be
joined together.
17. The internal combustion engine as claimed in claim 16, wherein
the piston bowl comprises a bottom wall and side walls which
cooperate to define the generally V-shaped contour of the piston
bowl, the bottom wall including opposed and inclined bottom wall
portions forming a V-shaped contour, the side walls being connected
with opposed outer peripheries of the bottom wall portions.
18. The internal combustion engine as claimed in claim 17, wherein
the side walls are inclined toward the central axis of the piston
crown.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an improved piston for an internal
combustion engine which is adapted to create a tumble flow of
intake air in the combustion chamber for mainly attaining a
stratified charge combustion.
U.S. Pat. No. 6,220,215 B1 discloses a piston for an in-cylinder
direct injection gasoline engine which has a recess in the piston
crown. Tumble flows of intake air introduced into a combustion
chamber in an engine cylinder are created in the recess, and fuel
injected into the combustion chamber is entrained on the tumble
flows. A stratified charge flow of air-fuel mixture is thus formed
and directed toward a spark plug.
SUMMARY OF THE INVENTION
However, since the recess of the piston crown in the
above-described earlier technology has a plane bottom surface, the
following problem tends to occur. If such a piston as described in
the above-described earlier technology is employed in an
in-cylinder direct injection engine having two intake valves and
adapted to create two parallel tumble flows of intake air, the
tumble flows will not be adequately adjusted at large flow velocity
of the tumble flows under the high-speed engine operation. Cycle
variation in flow velocity or turbulence of the tumble flows will
be increased, and a flow of air-fuel mixture will be fluctuated to
thereby fail to direct the tumble flows toward the spark plug. This
causes deterioration of combustion stability of the engine.
There is a demand to solve the above-described problem. An object
of the present invention is to improve combustion stability of an
in-cylinder direct injection engine by retaining two parallel
tumble flows at a stable state from a compression stroke of a
piston to a combustion stroke thereof.
According to one aspect of the present invention, there is provided
a piston for an internal combustion engine, comprising: a piston
crown having a central axis; and a piston bowl disposed in the
piston crown, on which two tumble flows of air are provided, the
piston bowl having a contour in section taken along a vertical
plane intersecting the tumble flows, the contour including an
inclined portion inclined toward the central axis of the piston
crown, the two tumble flows being disposed at the inclined
portion.
According to a further aspect of the present invention, there is
provided a piston for an internal combustion engine, comprising: a
piston crown having a central axis; and a piston bowl disposed in
the piston crown, on which two tumble flows of air are provided,
the piston bowl including a bottom wall and opposed and inclined
side walls connected with the bottom wall, the side walls being
opposed to each other and inclined toward the central axis of the
piston crown.
According to a still further aspect of the present invention, there
is provided a piston for an internal combustion engine, comprising:
a piston crown including an intake side and an exhaust side; and a
piston bowl disposed in the piston crown, the piston bowl having a
generally V-shaped section taken along a vertical plane
perpendicular to a direction extending from the intake side of the
piston crown toward the exhaust side thereof.
According to a still further aspect of the present invention, there
is provided an internal combustion engine, comprising: a cylinder
chamber; a cylinder head enclosing the cylinder chamber; a piston
within the cylinder chamber, the piston cooperating with the
cylinder chamber and the cylinder head to form a combustion
chamber; at least two intake ports in the cylinder head,
communicating with the combustion chamber to introduce air into the
combustion chamber; at least two exhaust ports in the cylinder
head, communicating with the combustion chamber; an intake air
control valve in each of the at least two intake ports, operative
to deflect the air and create two tumble flows of the air in the
combustion chamber; a fuel injector in the cylinder head, operative
to directly inject fuel into the combustion chamber; a spark plug
in the cylinder head, operative to ignite an air-fuel mixture in
the combustion chamber; wherein the piston includes: a piston crown
having a central axis; and a piston bowl disposed in the piston
crown, on which the two tumble flows of air are provided, the
piston bowl having a contour in section taken along a vertical
plane intersecting the tumble flows, the contour including an
inclined portion inclined toward the central axis of the piston
crown, the two tumble flows being disposed at the inclined
portion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical cross-section of an in-cylinder direct
injection engine to which a piston according to a preferred
embodiment of the present invention, is incorporated, showing a
combustion chamber structure;
FIG. 2 is a schematic diagram showing arrangement of the engine
parts around the combustion chamber as viewed from a lower
side;
FIG. 3 is a top plan view of the piston;
FIG. 4 is a cross-section taken along line 4--4 of FIG. 3;
FIG. 5 is an explanatory-diagram showing function in the preferred
embodiment in comparison with that in an earlier technology;
FIG. 6 is a graph showing a relationship between strength of tumble
flows of intake air and cycle variation of flow velocity of the
tumble flows in the preferred embodiment, and the similar
relationship in an earlier technology;
FIG. 7 is a graph showing a relationship between engine operating
ranges and cycle variation of combustion period in the preferred
embodiment, and the similar relationship in an earlier technology;
and
FIG. 8 is a map showing combustion regions relative to the engine
operating conditions.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT
Referring now to FIGS. 1 to 4, a piston of the present invention,
which is incorporated into an in-cylinder direct injection engine,
is explained.
As illustrated in FIG. 1, the in-cylinder direct injection engine
includes cylinder block 10 and a plurality of cylinder chambers or
bores 14 disposed in cylinder block 10. Cylinder head 12 is mounted
onto cylinder block 10 to enclose cylinder chambers 14. A plurality
of pistons 16 each are disposed coaxially with corresponding
cylinder chambers 14 and slidably fitted thereto, only one of which
is shown for illustrative purposes. Four-valve cross-flow pent roof
combustion chamber 32 is defined by cylinder block 10, cylinder
head 12 and piston crown 18 of piston 16. Cylinder head 12 is
formed with a pair of intake ports 22 corresponding to a pair of
intake valves 24, and a pair of exhaust ports 36 corresponding to a
pair of exhaust valves 26. Intake ports 22 communicate with
combustion chamber 32 to introduce air into combustion chamber 32.
Exhaust ports 36 communicate with combustion chamber 32 to exhaust
air-fuel mixture burned within combustion chamber 32. One pair of
intake ports 22 and intake valves 24, and one pair of exhaust ports
36 and exhaust valves 26 are shown in FIG. 1. Spark plug 30 is
disposed in a middle wall portion of cylinder head 12 near the
central axis of cylinder chamber 14. Spark plug 30 is positioned
near an upper center portion of combustion chamber 32 which is
surrounded by intake valves 24 and exhaust valves 26 as shown in
FIG. 2. Intake air control valve 34 is disposed within each of
intake ports 22 as shown in FIG. 2. Intake air control valve 34 is
operated depending on engine operating conditions via an actuator,
not shown, so as to move between an open position and a closed
position. Intake air control valve 34 is moved to the closed
position in a predetermined engine operating range explained later.
In the closed position, intake air control valve 34 closes a part
of intake port 22 and deflects the intake air flow directed toward
combustion chamber 32 so as to create tumble flow (generally
vertical vortex of air) T of the intake air within combustion
chamber 32. Two tumble flows T of the intake air introduced from
intake ports 22 are thus generated within combustion chamber 32 as
shown in FIG. 2. In the predetermined engine operating range
described above, an engine speed is not more than 3600 rpm and an
engine load is 500-700 kPa (brake mean effective pressure). The
engine operating range corresponds to a stratified combustion
region squared in FIG. 8, in which a stratified charge combustion
is attained. Fuel injector 28 is installed in a lower wall of
cylinder head 12 as shown in FIG. 1, and located at a middle
position between two intake ports 22 as shown in FIG. 2. Fuel
injector 28 is designed to inject fuel spray into combustion
chamber 32 in such a direction that the fuel spray is entrained on
two tumble flows T and guided to near spark plug 30.
Piston bowl 20 is disposed in piston crown 18 of piston 16, on
which two tumble flows T are provided. Piston bowl 20 has a
generally V-shaped contour in section taken along a vertical plane
intersecting two tumble flows T, as shown in FIG. 4. Namely, the
vertical plane is located perpendicular to a direction extending
from the intake side of piston crown 18 toward the exhaust side
thereof. As illustrated in FIG. 4, the contour includes an inclined
portion inclined toward central axis X of piston crown 18. The
inclined portion includes two opposed linear portions that extend
linearly and inclinedly toward central axis X of piston crown 18 so
as to gradually increase a depth of piston bowl 20. Two tumble
flows T are located at the inclined portion as shown on the right
side column of FIG. 5. Two tumble flows T are positioned downward
in a direction of central axis X of piston crown 18 because of the
increased depth of piston bowl 20.
Specifically, as seen from FIGS. 3 and 4, piston bowl 20 includes
bottom wall 20A and side walls 20B connected with bottom wall 20A.
Bottom wall 20A and side walls 20B cooperate to define the contour
of piston bowl 20 as shown in FIG. 4. As illustrated in FIG. 3,
bottom wall 20A includes bottom wall portions 20A1 and 20A2
extending from the intake side of piston crown 18 toward the
exhaust side along tumble flows T. Bottom wall portions 20A1 and
20A2 are connected with each other at junction L shown in FIG. 3.
Piston bowl 20 is positioned in a central portion of a top surface
of piston crown 18 such that junction L of bottom wall portions
20A1 and 20A2 extends substantially across central axis X of piston
crown 18. As shown in FIG. 4, bottom wall portions 20A1 and 20A2
are opposed to each other and inclined toward central axis X of
piston crown 18. Bottom wall portions 20A1 and 20A2 define a
V-shaped contour forming a part of the generally V-shaped contour
of piston bowl 20. Bottom wall portions 20A1 and 20A2 are inclined
at angle .theta.1, in this embodiment, approximately 7 degrees,
relative to horizontal plane P1 of piston crown 18. Here,
horizontal plane P1 of piston crown 18 means a plane perpendicular
to central axis X of piston crown 18. Due to the inclination of
bottom wall portions 20A1 and 20A2, two tumble flows T is retained
thereon at an inclined state inclined toward central axis X of
piston crown 18.
Side walls 20B are connected with opposed outer peripheries of
bottom wall portions 20A1 and 20A2, respectively. Side walls 20B
are opposed to each other and inclined toward central axis X of
piston crown 18. Side walls 20B form inwardly inclined contours
continuing with the V-shaped contour formed by bottom wall portions
20A1 and 20A2, which is a remaining part of the generally V-shaped
contour of piston bowl 20. Side walls 20B are inclined at angle
.theta.2, in this embodiment, approximately 10 degrees, relative to
plane P2 perpendicular to horizontal plane P1 and parallel to
central axis X of piston crown 18. Side walls 20B retain tumble
flows T at the inclined state therealong.
As illustrated in FIG. 1, piston bowl 20 has a generally
sector-shaped section taken along a vertical plane that is
substantially parallel to two tumble flows T. Bottom wall 20A
defines an arcuate contour in section as shown in FIG. 1, which is
roundly curved along streamlines of tumble flows T.
Referring to FIGS. 5-7, functions and effects of the piston of the
present invention are explained in comparison with those of a
piston in an earlier technology. In FIG. 5, the piston in the
earlier technology is shown on the left side column of the figure,
and the piston of the present invention is shown on the right side
column. The piston in the earlier technology has the piston bowl
whose bottom is defined by a planar surface. As illustrated on the
upper part of the left side column of FIG. 5, two tumble flows of
intake air within the combustion chamber are generated at an
upright state on the piston bowl of the piston in parallel relation
to the central axis of the piston crown at an early stage of the
compression stroke. When the piston moves from the early stage
position to a near-TDC position approximately 40 degrees before top
dead center (TDC) as shown on the lower part of the left side
column of FIG. 5, the inclination direction of each of the two
tumble flows is indefinite and the tumble flow fluctuates. Due to
the planar bottom surface of the piston bowl in the earlier
technology, the unstable tumbling behavior of the two tumble flows
is caused during the compression stroke of the piston.
Generally, near the TDC at a late stage of the compression stroke
of the piston, stream of the tumble flow within the combustion
chamber breaks and produces turbulence. Here, if a relatively
strong turbulence is generated in the combustion chamber, rapid
combustion of air-fuel mixture can be attained. Also, the strong
turbulence entrains the fuel spray injected at the late stage of
the compression stroke, to near the spark plug, so that a
stratified charge combustion can be achieved. However, in the
piston in the earlier technology as shown on the left side column
in FIG. 5, the above-described unstable tumbling behavior of the
tumble flows is caused when strong tumble flows are provided upon
the engine operation at high load or high speed. This will cause
large cycle variation or fluctuation of flow velocity or turbulence
of the tumble flows as indicated by curve 200 in FIG. 6, and large
cycle variation or fluctuation in fuel entrainment by the tumble
flows to near the spark plug.
On the other hand, as illustrated on the upper part of the right
side column of FIG. 5, two tumble flows of intake air which is
created within the combustion chamber are disposed at an inclined
state on the piston bowl of the piston of the present invention at
the early stage of the compression stroke. This is because piston
bowl 20, that includes V-shaped bottom wall 20A and inwardly
inclined side walls 20B as explained above with reference to FIG.
4, restricts the inclination direction of the two tumble flows.
Further, as shown on the lower part of the right side column of
FIG. 5, even at the near-TDC position in the compression stroke of
the piston, the tumble flows can be stably retained at the inclined
state, so that stable stream and turbulence of the tumble flows can
be produced. This will reduce cycle variation of flow velocity or
turbulence of the tumble flows relative to tumble strength as
indicated by curve 100 in FIG. 6, which is smaller than the cycle
variation thereof in the earlier technology. The piston of the
present invention can provide the stable flow of air-fuel mixture
directed to near the spark plug during the compression stroke,
which serves for achieving a stable combustion at the combustion
stroke. Further, owing to the configuration, i.e., the V-shape in
section, of the piston bowl of the piston of the present invention,
a space between the spark plug and the bottom of the piston bowl is
increased as compared with the space therebetween formed in the
piston bowl in the earlier technology. A flame generated upon
combustion of the air-fuel mixture in the combustion chamber can be
better grown in the increased space, so that the combustion period
can be reduced.
FIG. 7 shows cycle variation of combustion period relative to
engine operating ranges as indicated by broken line 300, which is
exhibited in the case of using the piston of the present invention.
As illustrated in FIG. 7, the cycle variation of combustion period
as indicated by broken line 300 is smaller than the cycle variation
thereof indicated by line 400, which is exhibited in the case of
using the piston in the earlier technology as shown on the left
side column in FIG. 5. In the case of using the piston of the
present invention, the cycle variation of combustion period is
significantly reduced in the medium speed and medium load range of
the engine operation. The medium speed and medium load range is
indicated by hatching in FIG. 8.
Accordingly, the in-cylinder direct injection internal combustion
engine using the piston of the present invention can ensure
transportation of fuel spray injected from the fuel injector to
near the spark plug and attain stable ignition of the air-fuel
mixture to thereby exhibit good combustion stability.
This application is based on prior Japanese Patent Application No.
2001-004875 filed on Jan. 12, 2001, the entire contents of which
are hereby incorporated by reference.
Although the invention has been described above by reference to a
certain embodiment of the invention, the invention is not limited
to the embodiment described above. Modifications and variations of
the embodiment described above will occur to those skilled in the
art in light of the above teachings. The scope of the invention is
defined with reference to the following claims.
* * * * *